There are several distinct technological approaches for generating a visible light display, particularly large size displays such as those characterized as large screen televisions. Liquid crystal displays generally exhibit high resolution and advantageous thinness (e.g., about 3 inches). These are typically limited to sizes of 42″(diagonal) or less due to cost constraints and the fact that a drive current cannot be easily maintained along a very long amorphous silicon row or column drive line, requiring significantly complex drive electronics. Liquid crystal displays suffer from the drawback that a single pixel can significantly deteriorate resolution over the entire display; large sheets of glass have fewer large panels, so the yield loss is highly non-linear and decreases with display size.
Another technology for large displays is plasma television, commonly commercially available in the range of 42 to 50 inches. While plasma offers good thinness (e.g., 4 inches) and a wide viewing angle, resolution is not as sharp as other technologies, the expensive addressing electronics balance bit depth against resolution rather than maximizing both, they are generally heavier and suffer from ‘burn in’ at the display screen over time, and they suffer from the same single-pixel shortfall as liquid crystal displays. While some research is ongoing into using organic LEDs (OLEDs) in large displays, these typically have a lifetime of about 8000 hours or less for such high-power applications and are seen as inherently limited.
Front and rear projection television is becoming more popular as they overcome some of the above problems with liquid crystal and plasma technologies. Projection systems enable screen sizes of 100 inches or greater, and typically suffer from resolution and/or brightness (e.g., contending with ambient light for a very large screen). Light valves are at the heart of projector systems, mixing shades of different colored light (e.g., red, green and blue) to produce a full spectrum of color in the displayed image. High temperature polysilicon (HTPS) implementations, such as those marketed by Seiko, Epson and Sony, generally use an arc lamp for illumination yet still exhibit low brightness at the display due to aperture constraints (ratio of light to area of reflection) and parasitic diffraction. Further, resolution in the more commercially popular models is no better than that of plasma.
Liquid crystal on silicon (LCoS) light valves are used by Sony, JVC, and a host of other manufacturers, in a relatively small segment of the large display market. While these improve brightness and even resolution over HTPS technology for little additional cost, they also use an arc lamp for illumination to overcome light losses between the arc lamp and the display. It is not unusual for light losses in LCoS to be 35% or more, due to aperture, parasitic diffraction, and aluminum reflectivity. The inventors see such losses as inherent in the LCoS technology, because much light is lost between ‘tiles’ (typically discrete aluminum reflectors) and an even greater amount is lost by diffraction from those tile boundaries.
Digital light processing (DLP), a technology for which Texas instruments is well known, also uses an arc lamp and generates mid-range brightness but lesser resolution than LCoS. DLP exhibits even higher light losses than LCoS, due to a spinning ‘color wheel’ in addition to micro-reflectors that impose loses similar to the LCoS tiles. The color wheel is seen as necessary for DLP in order to operate with a single light valve; multiple light valves for different colors are seen to drive costs high enough that DLP would not be commercially competitive with other technologies.
Each of HTPS, LCoS and DLP dispose the addressing electronics directly below the modulating surface. This leads to two competing concerns. First, large area CMOS dies for the drive electronics are highly expensive; increasing CMOS chip size is highly non-linear with cost. Second, optics require that the modulating surface be large enough to collect sufficient light to drive a large display with sufficient resolution and brightness. The confluence of drive electronics and the modulating plane as above result in low yield and high cost for manufacturing HTPS, LCoS and DLP projectors. What is needed in the art is a technology that enables large screen displays (e.g., greater than about 42 inches) with good resolution and brightness, without the tradeoffs above between the size of the CMOS chip and the optical modulating surface that drive up costs in the current technology.